As air flows through a duct, such as a tube or hose, it loses kinetic energy, in the form of pressure, due to friction. Such pressure drop is a function of a number of different factors, including the shape and size of the duct and its length.
In an air seeder utilizing a pneumatic conveyance system, the success of the system is dependent upon maintaining an adequate amount of airflow throughout the system to keep the seeds in suspension within the air stream. If the airflow is insufficient, the product will fall from the stream and begin to build up on the bottom of the tube or hose. If the condition persists, the airflow within the tube or hose will be reduced to zero, and the build up of seeds will eventually cause plugging.
Typically, all hoses on an air seeder are supplied by a common air source and the flow is split equally among the various hoses, which are of the same size and shape. However, the sufficiency of the airflow can be an issue if the hoses vary in length, in order to reach openers on the machine that are unequally spaced from the air source. The different pressure drops caused by differences in hose length may result in plugging or uneven distribution of the seeds among the openers.
One way of keeping the pressure drop uniform throughout all hoses is to equalize their lengths. However, this means that hoses which deliver to locations closer to the source than others will necessarily have surplus lengths that are not needed, except for pressure uniformity purposes. This surplus hosing increases costs, stretches out set up and assembly time, wastes space, and looks cluttered and unattractive.
The present invention allows all the hoses to be as long or as short as necessary to reach their particular locations on the machine, without causing different pressure drops due to the different lengths. Internal airflow restrictors are utilized in the shorter hoses to create pressure drops to match those of the longer hose lengths. Different size restrictors are utilized in different hoses, depending upon the amount of pressure drop required to establish uniformity throughout all hoses.
In a preferred embodiment of the invention, the necessary flow restrictors are incorporated into a coupling assembly which detachably joins hoses from the seed reservoir cart with primary hoses on the seeding implement itself. Nipples on the coupling assembly may be fitted internally with appropriately dimensioned restrictors so that the restrictors are essentially hidden from view and require minimal maintenance.